Food casings of regenerated cellulose are widely used for the production of various stuffed food products. The present invention is concerned primarily with thin walled unreinforced cellulosic casing as may be used in the production of small diameter sausages such as frankfurters and the like.
For convenience of handling, food casings which may be 20 to 50 meters or more in length are shirred and preferably compressed to produce what commonly are referred to as "shirred casing sticks". Shirring machines for producing these shirred sticks are well known in the art and are disclosed in U.S. Pat. Nos. 2,983,949 and 2,984,574 among others. Shirring and related technology also are described in the Noyes Data publication "Sausage Casing Technology" by Karmas (1974) at pages 259-347.
Cellulosic casing for the shirring operation is supplied in reels. Flat casing feed stock, drawn from the reel, is fed into a shirring machine where it is inflated with low pressure gas, usually air. The inflated casing is moved onto and along a mandrel and through a shirring zone where a shirring mechanism, usually an array of shirring rolls, gathers the casing about the mandrel into generally conical pleats nested one tightly against another. The inner folds of the pleats are formed against the mandrel and define the surface of an axial bore through the stick.
When a preselected shirred length has been attained, it is severed and moved longitudinally away from the array of shirring rolls for further processing. Such further processing may include, for example, a compaction operation where the shirred length is reduced and an operation where a closure is formed and inserted to stop or plug the bore at one end of the casing thereby forming a "closed" end. The other end of the casing is left open to permit mounting of the shirred stick onto a stuffing horn.
Severing a shirred length has been accomplished both manually and by automatic means after, i.e., downstream of the shirring zone. For example, one general method is to wait until some length of shirred casing has accumulated and then separate off a desired length from this accumulated shirred length as disclosed for example in U.S. Pat. No. 3,112,517. Another general method is to shirr only a desired length and then separate this shirred length from the feed stock. This general method is disclosed for example in U.S. Pat. Nos. 3,936,909; 4,547,932 and 4,885,821 among others.
Whatever the severing means, it is desired that the casing be cut cleanly to avoid so called "shards" or "flags" which are ragged pieces of casing attached to one or both the severed ends. When tensioning is relied upon to sever the casing shards are often formed on one or both of the , severed ends. U.S. Pat. No. 4,885,821 illustrates that in a casing under tension, a tear, which initiates at some point on the casing, propagates in opposite directions around the casing. If the ends of the tear propagation fail to meet in the same transverse plane, they overlap and run past one another. As the tear continues to propagate, one end of the tear eventually will run into the other which causes a loose piece or so called "shard" or "flag" of casing to form on one of the severed ends. If tears initiate at a plurality of points around the casing, then several shards may be formed.
Shards at the severed ends of the casing are objectionable because they may separate from the casing and become incorporated into the food product being stuffed into the casing. This is especially the case when using the casing for stuffing frankfurters. After a shirred stick is stuffed with a frankfurter emulsion, it is common for the operator to squeeze out or "milk" emulsion from the ends of the casing so the ends can be tied off. When this is done, shards at the end of the casing can rip free. Since the emulsion squeezed out of the casing is recovered and recycled, any shard of casing ripped off by the procedure may become incorporated into the emulsion supply.
Accordingly, it is most desirable to sever the shirred stick from casing feed stock in a manner which at least reduces the size of shards on the severed ends of casing, and preferably eliminates their formation.
Various severing methods have been proposed to reduce the instances of forming shards on the ends of the severed casing. For example, U.S. Pat. No. 4,885,821 discloses a severing apparatus wherein closing three arcuate members about the shirring mandrel provides a knife edge in the form of a closed circle at a location after, i.e., downstream of the shirring zone. This edge is pressed against the end face of the shirred stick to push the stick longitudinally along the mandrel and this causes the feed stock to tear away along the knife edge.
In U.S. Pat. No. 3,936,909 three arcuate members, also located downstream of the shirring zone, are closed about the circumference of an inflated section of the feed stock casing close to the end face of the shirred stick. The arcuate members form a closed circle about the casing and weakens the casing either by heating or by perforating it about substantially the full circumference of the casing. Subsequent longitudinal displacement of the shirred casing along the mandrel will cause the feed stock to separate from the stick at the weakened section.
The operation of closing arcuate members about the casing presents certain problems. For example, if the casing and arcuate members are not on the same center, the casing may not be uniformly severed so that shards on one or both severed ends results. Also, the casing which passes through the shirring zone is creased and folded. Accordingly, severing after the shirring zone may involve a casing that is not uniformly round. This means that the arcuate members closing about the casing may not uniformly engage the casing circumference, or a casing crease or fold may become pinched between adjacent arcuate member. As a further problem, tears initiated about the circumference of the creased casing may tend to follow along the fold or crease lines and this interferes with the formation of a clean, shard-free transverse severing of the casing.
In the present invention, severing occurs after or downstream of the shirring zone. However, problems associated with the proper closing of arcuate members about the casing and shirring mandrel as well as the severing problems associated with attempting to sever casing creased and folded by shirring are minimized by preparing the casing feed stock for severing prior to entering the shirring zone.
In particular, the casing is prepared by weakening the feed stock along a narrow transverse band at a defined location along its length prior to entering the shirring zone. After the casing moves through the shirring zone, a tensile stress applied to the feed stock casing will easily sever it at the weakened area.